Effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field

Abstract

The effect of neutral pressure on blue core in Ar helicon plasma under inhomogeneous magnetic field was investigated in this work. The neutral pressure was set to 0.08 Pa, 0.36 Pa and 0.68 Pa. Nikon camera, intensifies charge coupled device (ICCD), optical emission spectrometer (OES), and Langmuir probe were used to diagnose the blue core in helicon plasma. Helicon plasma discharges experienced density jumps from E-, H- to W-mode before power just rose to 200 W. The plasma density increased and maintained the central peak with the increase of neutral pressure. However, the brightness of the blue core gradually decreased. It demonstrated that the relative intensity of Ar II spectral lines and the ionization ratio in the central area were reduced. Radial electron temperature profiles were flattened and became hollow as neutral pressure increased. It demonstrated that increasing the neutral pressure weakened the central heating efficiency dominated by helicon wave and strengthened the edge heating efficiency governed by the TG wave and skin effect. Therefore, the present experiment successfully reveals how the neutral pressure affects the heating mechanism of helicon plasma in inhomogeneous magnetic field.

Effect of antenna helicity on discharge characteristics of helicon plasma under a divergent magnetic field

“…The wavelength determined by the unbounded dispersion equation (10) for whistler waves under RH helical antenna excitation is about 1.72 cm, and the wavelength of LH helical antenna excitation is about 3.34 cm. This is also consistent with higher-density operation according to the dispersion relation of the helicon wave [51]. The energy deposition mechanisms for helicon plasmas mainly consider coupling to TG (electron cyclotron) modes, which, being quasi-electrostatic, are rapidly absorbed as they propagate inward from the radial boundary.…”